1. Field of the Invention
This invention relates to a gantry robot construction and to a drive mechanism useful for a gantry robot. More particularly, it relates to a construction which increases the speed and efficiency of a gantry robot.
2. Description of the Related Art
Robots are used in a variety of applications. A robot can perform repetitive tasks, such as welding, sealing, gluing, water-jet and laser cutting, and material handling with reliability and accuracy.
A robot must be placed in the area of the product to be manufactured or handled. This area is called the "work area". There are basically two methods of placing robots in a work area. The first is by placing the robot on a rotary pedestal which is operatively associated with a track. The robot is moved in and about the work area by controlling its motion on the pedestal and track. The disadvantage of this type of robot is that the working area or "envelope" in which it can operate is rather limited.
The second method of placement and the one with which this application is concerned, is by using a gantry construction. Gantry robots are typically of the "standard bridge type" and are mounted overhead the work area or envelope. The standard bridge gantry construction consists of a pair of spaced parallel beams or rails mounted on floor supports that suspend the rails from the ground or shop floor. A bridge spans the distance between the rails and is movable relative to the rails. The robot is comprised of a robot support which is movable with respect to the bridge and a robot head attached to the support. The robot head performs the desired task.
As discussed above, the robot operates in a work area or envelope. This work area is usually in the form of a rectangular box having a length, width, and height. The robot is able to reach any point within this area because of the arrangement of the rails, bridge, and robot head. The rails provide a lengthwise axis on which the bridge can move. Thus any point along the length of the work area can be reached. The robot, because it is movable with respect to the bridge, can reach any point along the width of the work area. In addition, the robot support and therefore the robot head can move up and down, so that any height in the work area can be reached.
For convenience of reference, the work area is said to have a length of dimension X, a width having dimension Y, and a height Z, with dimension X being greater than Y. The usual practice in constructing gantries has been to place the rails (or a single suspended rail) on the two long sides (or side) (X-axis) so that the bridge will have a dimension of Y and thus span the Y-axis. See, e.g., U.S. Pat. Nos. 457,441, 1,694,084, 1,975,094, 3,884,363, 4,561,551, and 4,571,149 and U. K. Patent Application Nos. 2,120,202A and 2,176,168A. In fact, U.S. Pat. Nos. 3,116,586 and 4,642,017 teach that the rails should extend the length of the shop floor or the yard in which an overhead crane operates.
The reason for the conventional configuration of the crane is to keep the bridge, which is the heaviest movable component, to the lowest possible weight. This is done by having the bridge span the lesser Y dimension. This design results in reducing the mass which must be accelerated to move from one point to another. If a robot is used with a gantry of conventional designs, the bridge will move the longer distance on the X-axis and the robot will move the shorter distance on the Y-axis.